When torque is applied to a shaft, stress is applied along helical lines of compression and tension along the surface of the shaft. Various methods are known for measurement of the torque in a shaft. One method is to bond strain gauges to the exterior surface of the shaft with the strain gauges positioned in a cross configuration. The strain gauges function as elements of a resistive bridge circuit measuring compression and tension in the shaft surface along their length as the shaft torsionally twists. Torque measurement in a rotating shaft can be a challenge to implement when using strain gauges as the sensing elements as the strain gauges necessarily need to interface electrically with other off-shaft electronics. The off-shaft electronics are necessary to perform the resistance bridge measurements so as to detect and quantify tension and compression resulting from torsional twisting of the shaft as indicative of transmitted shaft torque.
Transmitted torque in a shaft may also be determined by measurement of the angular displacement between two gears mounted to the shaft in a distally spaced relationship along the axis of rotation of the shaft. Using this method, the angular displacement between spaced gears is indicative of the twist angle over the length of the shaft between the gears, the twist angle being indicative of torque transmitted along the shaft.